Our objective is to characterize the cell cycle of corneal endothelium and to eventually identify the mechanism(s) which control entrance into the cycle. The study is to be conducted both in vivo and and in tissue culture. In the former type of work we will initiate hyperplasia by means of injury (usually by freezing). In the latter, addition of serum or other appropriate factors to the medium will serve as division stimuli. The timing of the onset of DNA synthesis and mitosis will be noted as well as changes in association of chromosomal proteins with DNA. The dependence of growth on RNA and protein synthesis will be determined. The chromosomal proteins are to be isolated from endothelial nuclei. Their behavior in different stations of the growth cycle will be followed. It is further proposed to examine the nature of the contribution to repair made by unusual division forms (amitosis, multipolar mitosis, multinucleate giant cells). The endothelium will be cultured in order to secure large numbers of synchronously dividing cells for biochemical analyses. Histochemical techniques to be used include autoradiography, microspectrophotometry and microfluorometry. Electron microscope studied may be pursued as well but these would be performed in collaboration with others. In vitro investigations will entail performance of gel electrophoresis. The work will start with frog, rat and rabbit corneas; we will endeavor to study human materials at a later stage of the project.